## Calculus 10th Edition

$\frac{x}{a}+\frac{y}{b}=1$
let $(a,0)$ $(x_{1},y_{1})$ let $(0,b)$ $(x_{2},y_{2})$ Use the formula $\frac{y-y_{1}}{y_{2}-y_{1}}=\frac{x-x_{1}}{x_{2}-x_{1}}$ $\frac{y-0}{b-0}=\frac{x-a}{0-a}$ $\frac{y}{b}=\frac{-(x-a)}{a}$ $\frac{y}{b}=-\frac{x}{a}+\frac{a}{a}$ $\frac{y}{b}=-\frac{x}{a}+1$ Therefore, $\frac{x}{a}+\frac{y}{b}=1$